Wideband RF Filters Using Medium-Scale Integration of Lithium Niobate Laterally Vibrating Resonators

Abstract

This letter presents wideband spurious-free microelectromechanical systems (MEMSs) filters based on shear horizontal (SH0) mode Lithium Niobate (LiNbO3) laterally vibrating resonators. The filters, monolithically fabricated on the same chip, have center frequencies at 400 and 750 MHz. The measured performance exhibits in-band ripple-free response, a low insertion loss (IL) of 1.7 dB, a 30-dB shape factor of 1.41, and a 3-dB fractional bandwidth (FBW) of 9.6 %-the largest reported for MEMS-resonator-based filters. The high performance was collaboratively enabled by the LiNbO3 material and filter design. The excellent piezoelectric coupling and low acoustic loss in LiNbO3 thin film ensure the low IL and large FBW, while the medium-scale integration of 200 spurious mode-free resonators fully harnesses the potential of LiNbO3 material without introducing spurious response. The filters have a device footprint less than $360 \times 350\,\,\mu \text{m}^{2}$ , thus suitable for RF frontends in handheld wireless devices.